1. Field of the Invention
The present invention relates to a photosensitive composition and an image recording material using the same. More particularly, the present invention relates to an infrared laser photosensitive composition that is suitable for a planographic printing plate precursor and the like for what is referred to as direct plate making, which allows plates to be directly produced based on digital signals from a computer or the like. The present invention further relates to an image recording material using the photosensitive composition.
2. Description of the Related Art
Recent development of lasers has been remarkable, and, in particular, progress is being made with respect to high output and miniaturization in solid-state lasers and semiconductor lasers having an emission region in the near infrared to infrared regions. Accordingly, such lasers are extremely useful as exposure light sources during the direct production of printing plates based on digital data from computers and the like.
Negative planographic printing plate precursors for infrared lasers are used with infrared lasers that emit infrared rays as exposure light sources. Such planographic printing plate precursors are employed in recording methods that produce an image portion through polymerization reaction with a radical generated by light or heat serving as an initiator, so as to cure a recording layer at an exposed portion thereof where the image portion is to be formed. Alternatively, in this method, when a dye is used as an infrared absorbent, a radical generated by electron-transfer from the dye that has absorbed the infrared ray is used as the initiator of the polymerization.
For use in such recording methods, combinations of resol resins, novolak resins, infrared absorbents and photoacid generators have been proposed, for example, in Japanese Patent Application Laid-Open (JP-A) Nos. 7-20629 and 7-271029. Further, combinations of specific polymers, photoacid generators and near infrared sensitizing dyes have also been proposed, for example, in JP-A Nos. 11-212252 and 11-231535.
However, with polymerizable compositions featuring the use of photopolymerization initiators or photoacid generators such as those described above, it is difficult to impart sufficiently high photosensitivity in the near infrared regions. The photosensitivity is particularly insufficient when such polymerizable compositions are applied to scanning exposure using infrared laser light.
Polymerization using photopolymerization initiators or photoacid generators is often insufficient with exposure to light alone. Thus, when the above-described polymerizable compositions are to be used in planographic printing plate precursors, heat processing is necessarily conducted after the precursor is exposed to light or developed, in order to accelerate and complete polymerization. The heat processing has therefore been among important steps during plate-making. However, the heat processing may become a cause of reduced production efficiency as well as unstable image quality. Potential problems involved in the heat processing are that, when the heating is insufficient, even portions which have been exposed to light are dissolved, and that, when the heating temperature is too high, portions which have not been exposed to light partially become insoluble, whereby non-image portions are insufficiently developed. Those problems may result from difficulty in maintaining a uniform difference in solubility between exposed portions and unexposed portions.
In order to solve such problems, photosensitive planographic printing plate precursors that can be subjected to scan-exposure without requiring heat processing or provision of an overcoat layer are proposed (see, for example, JP-A Nos. 2001-290271, 2002-278081, 2003-29408 and 2003-43687). However, these planographic printing plate precursors lack suficient storage stability and stability under safelight illumination.
Accordingly, an object of the present invention is to provide a photosensitive composition with high photosensitivity to infrared light, good storage stability and stability under safelight illumination, and an image recording material using the same.
Another object of the present invention is to provide an image recording material suitable for a planographic printing plate precursor with good plate-comparability after plate-making.